APEX: A New Tool for Predicting the Effects of Climate and CO2 Changes on Erosion and Water Quality

Several field scale hydrologic/water quality models have been developed to study the impacts of agricultural management practices. The EPIC (Environment Policy Integrated Climate — previously the Erosion Productivity Impact Calculator) model is one of the more popular models, which has been widely applied in the United States and around the world. Such models are limited to small field size areas, where the soil; management, crop, and topography are assumed to be homogeneous. To extend the capabilities of EPIC to simulate large complex fanning systems (multiple fields, soils, rotations, management, etc.), a model called APEX (Agricultural Policy/Environmental eXtender) was developed. In addition to the capabilities of EPIC, APEX has components for routing water, sediment, and chemicals (nutrients and pesticides) across complex landscapes and channel systems to the watershed outlet. The subsurface routing routine to APEX is enhant;ed from that in EPIC and can be used to simulate subsurface processes to a depth of 30 m. In this paper we present an overview of EPIC and APEX, and describe in detail the recently added CO2 component of the model.

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